Method and apparatus for investigating earth formations traversed by boreholes



Nov. 16, 1 954 METHOD AND APPARATUS FOR I FORMATIONS TRAVERSED Filed Dec. 18, 1950 FIGJ.

M. SCHLUMBERG S ATING EARTH BOREHOLES 3 Sheets-Sheet 1 INVENTOR.

MARCEL SCHLUMBERGER HIS ATTORNEYS.

Nov. 16, 1954 MBERG 2,694,791 0 S ATING EARTH BOREHOLES M. SCHLU METHOD AND APP ATUS F R INVE FORMATI TRAVERSED BY Filed DEC. 18, 1950 5 Sheets-Sheet 2 INVENTOR.

MARCEL SCHLUMBERGER WfieefM HIS ATTORNEYS.

Nov. 16, 1954 M. SCHLUMBERGER 2,694,791 METHOD AND APPARATUS FOR INVESTIGATING EARTH FORMATIONS TRAVERSED BY BOREHOLES 3 Sheets-Sheet 3 Filed Dec. 18, 1950 n a & m F

FIGJO.

United States Patent Ofiiice 2,694,791 PatentedNov. 16, 1954 METHOD AND APPARATUS FOR INVESTIGATING IEARTH FORMATIONS TRAVERSED BY BORE- OLES Marcel Schlumberger, Paris, France, assignor to Societe de Prospection Electrique Procedes Schlumberger, Paris, France, a corporation of France Application December 18, 1950, Serial No. 201,333 Claims priority, application France March 17, 1950 19 Claims. (Cl. 324-1) This invention relates to'oil detection. More particularly, it is concerned with new and improved methods and apparatuses for detecting the presence of oil in aqueous media such as, for example, oil contained in petroleum bearing formations traversed by a well containing a column of drilling mud'orother aqueous liquid.

My copending application Serial No. 22,466, filed April 21, 1948, for Method and Means for Studying Rocks Throughout a Boring, discloses novel oil detecting methods and apparatuses in which samples of the contents of earth formations traversed by a bore hole may be obtained continuously at different depths in the hole. In one embodiment, this is accomplished by moving through the'bore hole a support carrying sample removing means which is maintained in frictional engagement with the wall of the bore hole. The sample removing means may comprise a wheel which rubs against successive portions of an elongated thread sample collector, or it may be a portion of the thread which rubs against the formations. Samples of the liquid contents of the formations, if any, thus removed by the sample removing means, are examined at the surface of the earth for the presence of oil or'other hydrocarbons.

The present invention is addressed to'novel methods and apparatuses of this character which enable samples removed from earth formations traversed by a bore hole to be tested for hydrocarbon content without the necessity for removing them from the bore hol'e.

Accordingly, it is an object of the invention to provide new and improved methods and apparatuses for detecting the presence of oilin aqueous media.

Another object of the invention is to provide new and improved oil detecting methods and apparatuses which are particularly adapted for surveying wells drilled into the earth, and which will provide substantially instantaneous indications of the presence of oil at various depths in a well, as well as facilitating a continuous, uninterrupted survey of the entire well or a portion thereof.

The above and other objects and features of the invention may be attained by disposing in the medium to be tested an accumulating member having a working surface formed of a water-repellent substance having a particular afiinity for oil, together with detecting means responsive to a characteristic property of 'any substance accumulated on the accumulating member for providing one signal when said substance is aqueous in nature, and a different signal when said substance is oil.

More specifically, the accumulating member may comprise an assemblage of conducting or partially conducting elements and insulating elements having 'a particular aflinity for oil disposed in such fashion that, when the latter collect a sufficientnumber of oil particles, an insulating screen of oil is formed in front of the exposed surfaces of the electrical conducting elements. The presence or absence of oil particles on the accumulating member is determined,"aecording to the invention, by obtaining indications of the electrical resistance'of a path including the conducting elements in'the accumulating member.

In a preferred form, the accumulating member comprises a plurality of electrically conducting elements or points embedded in an insulatingbody having a particular aflinity for oil in the presence of an aqueous medium, only the probe tips being exposed and lying fiush with the working surface thereof. With this construction, as an oil film is attracted to the working surface of the accumulating member, it will eventually, when a preestablished quantity of oil is present, bridge the gaps between the tips of the conducting points and insulate the latter from ground. Alternatively, the accumulating member may comprise a semiconducting or conducting agglomeration of electrical insulating material having an affinity for oil, and electrical conducting particles such as bits of metal or carbon, the whole being essentially an electrical conductor, the surface of which may nevertheless attract a film of oil to insulate momentarily the entire member from ground.

Thus, the invention utilizes the insulating properties of oil films as a means for determining the presence of oil, notwithstanding the fact that the latter may be present in admixture with other media such as water which would ordinarily disguise its presence.

According to the invention, the accumulating member may be constituted of various materials and in various forms so that it may engage the media to be analyzed in either sliding or rolling movement. Alternatively, the accumulating member may be spaced ashort distance from the media to be analyzed and various collector or feeder means provided for introducing successive specimens of the media to the accumulating apparatus in a continuous and mechanically efiicient manner as described in greater detail hereinafter.

Also according to the invention, an approximate quantitative analysis of the oil present in the various media may be obtained at any given depth in the well. This may be accomplished by providing conducting points of different relative sizes as compared to the working surface or surfaces of the accumulating member of which they are a part. Thus, a small quantity of oil may be accumulated in amounts suflicient to bridge the ends of one set of conducting points but insufficient to bridge the ends of the other set. As a result, it is possible to determine the approximate quantity of oil present in the medium under analysis.

The invention may be better understood by reference to, the following description'taken in conjunction with the accompanying drawings showing several preferred embodiments of the invention by way of illustration thereof and in which:

Fig. l is a view in longitudinal section of an accumulating'member formed of a material'having an affinity for oil, and showing electrical conducting means embedded therein, according to the invention;

Fig. 2 is a view in transversesection of the accumulating member shown in Fig. 1 taken along the line 2-2 thereof;

Fig. 3 is a view in longitudinal section of oil detecting apparatus constructed according to the invention and lowered into a well containing a column of drilling rnud'or other aqueous medium;

Fig. 4 is a partial, enlarged view in longitudinal section showing a portion of the accumulating member of Fig. 2 and illustrating how droplets of oil picked up by the accumulating member form an insulating film of oil over theconducting elements embedded therein;

Fig. 5 is a view in longitudinal'section of a modification having an accumulating member which is adapted to roll over the wall surface of a well drilled into the earth; s

Fig; 6 is an enlarged view in transverse section of the accumulating member in the apparatus shown inv Fig. 5, taken along the line 6-6 thereof;

Fig. 7 is a partial view in longitudinal section of the accumulatingmernber shown in Fig. 6, taken along the line 7- 7 thereof;

Fig. 8 is a view in vertical section taken on the line 8-8 of Fig. 9 of a portion of an oil detecting apparatus comprising another embodiment of the invention;

Fig. 9 is a view'in verticalsection taken along the I line 9-9 of Fig. 8, the accumulating roller portion being shown in elevation;

Fig. 10 is a view in longitudinal section of a well and showing disposed therein a further modified form of the oil detecting apparatus and its carrier assembly; and

Fig. 11 is a fragmentary view in transverse section of the accumulating roller member employed in the apparatus shown in Fig. 10.

Referring to Figs. 1-3 of the drawings, which show a device for detecting oil "in formations traversed by a well, the apparatus includes an accumulating member having a body portion 21 formed of a water-repellant material having a particular affinity for oil in aqueous media. This material should have good mechanical resistance to wear and should be able to withstand temperatures as high as 150 C., for example, such as may be encountered deep in an oil well. Materials such as the tetrafluorethylene polymers, the monochlorotrifluorethylene polymers and the like, for example, are suitable for this purpose, although it will be understood that other materials having similar properties and characteristics may be utilized.

The body portion 21 is sandwiched between a pair of of side walls 22a and 22b (Fig. 2), these elements being secured together by screws (not shown), for example.

A plurality of electrical conducting elements 23, 23

and 23" etc., are embedded in the body portion 21, their respective extremities or terminal ends being disposed fiush with a flat working surface 24 formed on the body portion 21. Such ends may be in the neighborhood of one millimeter in diameter. Preferably, the conducting elements 23, 23 and 23", etc., are made of metal. The majority of metals seem to be suitable for the purpose, although the specific properties of the particular metal selected should be considered, 'having in mind the end sought.

Alternatively, and in lieu of the probes 23, 23' and 23", etc., the body member may be formed of an agglomeration of material having an affinity for oil and a multiplicity of electrically conducting particles such as bits of metal or carbon, for example. The dispersion of particles renders the entire body a conductor or semiconductor of electricity, but does not destroy its oil accumulating character.

In operation, the accumulating member 20 and particularly the working surface 24 thereof, is adapted to engage or be engaged by the media to be analyzed such as the earth formations 25 (Fig. '3) traversed by a well 26, drilled into the earth and containing an aqueous medium L such as drilling mud, for example. To effect engagement of the working surface 24 with the wall of the well, a carrier assembly 27 is provided which may comprise a weighted carrier member 28 suspended in the well by means of a cable 27' which may contain or be combined with an insulated electrical conductor (not shown). Suitable means (not shown) may be provided in conjunction withthe cable 27 for indicating the depth in the well at which the carrier is disposed, as is well known in the art. Thus, for example, the cable may be calibrated or a meter may be provided on the WlllCh or reel (not shown) which-is used to raise and lower the cable in the well.

A pair of curved spring members 29 and 30 are secured at their upper ends to a fixed pivot 31 carried by the upper end of the carrier member 28. The lower ends of the springs 29 and 30 are secured in a pin and slot connection indicated generally at 32 formed in the lower end of the carrier member 28. The spring members 29 and 30 are self-biased outwardly and tend to engage the wall of the well at diametrically spaced points. The accumulating member 20 is carried by the spring member 30 with its working surface 24 disposed outwardly to engage the wall of the well in rubbing engagement.

The inner ends of each of the electrical conducting elements 23, 23, 23" etc., extend within a cavity 33 (Fig. 1) formed at the rear of the accumulating member and bounded by the side walls 22a and 22b and the spring member 30. A conductor 34 electrically connects each of the probe members 23, 23, 23". etc., with the conductor (not shown) in the cable 27. In the event the alternative form of the accumulating member 1s used, comprising the semi-conducting agglomeration of electrically conducting particles and the material having an afiinity for oil in a given medium, the conductor .34 might be connected-directly to the back of the member.

)ne terminal of a suitable source of electrical energy, wh ch may be located at the surface of the earth and indicated generally at 35, is connected to the cable conductor and the other terminal is connected by means of a conductor 35' to an indicating instrument such as an ammeter'36 connected to ground at 37. Preferably, the source 35 generates alternating current so as to eliminate the effects of spontaneous potentials from the measurements. The readings of the ammeter 36 afford an indication of the characteristics of media picked up by the accumulating member 20 in the well, although it will be understood that various other indicating systems may be utilized for this purpose as will be understood from the following description of the operation of the system.

As the carrier assembly 27 is lowered into the well, the working surface 24 of the accumulating member is caused to rub against the wall of the well. This rubbing movement insures that the material in direct engagement with the working surface 24 will at all times be representative of the part of the well wall immediately adjacent the carrier, this for the reason that the rubbing operation tends to wipe from the working surface 24 all previously accumulated matter.

The action of the detecting member 20 may be better understood with particular reference to i Fig. 4. As shown, the working surface 24 of the accumulating member 20 is in engagement with the earth formation 25 constituting the wall of the well and, because a certain small amount of oil is present in the formation, oil particles have accumulated on the surface 24 to form a film 38. This is due to the inherent characteristics of the material of which the accumulating member 20 is formed, all as set forth above. This oil film first accumulates on the surface 24 to the exclusion of the metallic terminal ends of the electrical conducting elements 23, 23, 23", etc. As the oil accumulates in greater quantity, however, the film will begin to bridge across the ends of the conducting elements (i. e. the conducting elements 23" and 23 in Fig. 4). Eventually the ends of all of the conducting elements 23, 23", etc., will also be bridged.

In operation, a voltage from the source 35 is im pressed upon the circuit comprising the parallel connected conducting elements 23, 23', etc., the conductor 34, the conductor in thecable 27, the indicating instrument 36 andthe ground return circuit through the intervening earth formations. Because of the small size of the conducting elements 23, 23 etc., the resistance of this circuit is constituted essentially by the contact resistance between the conducting elements 23, 23', etc., and the adjacent formations. When the formations do not contain oil, this resistance is a function primarily of the resistivity of the medium which lies immediately before the detecting surface 24. On the other hand, if the formations do contain oil, each of the conducting elements 23, 23, etc., is insulated from ground by the presence of an oil film 38, with the result that the resistance of the circuit between the voltage source 35 and ground through the conducting elements will suddenly increase considerably, thereby decreasing substantially the current in the circuit. The response of the indicating instrument 36 at the surface of the earth, therefore, will indicate that oil is present in certain quantities in the earth formation at that particular level in'the well.

A small droplet of mud or other aqueous medium 38' may be'trapped at the ends of the conducting elements, as illustrated in the' case of the elements23" and 23' in Fig. 4. This does not adversely affect the operation of the device, as the entrained drops38 are completely insulated from ground by the overlying oil film 38.

As soon as the apparatus leaves the medium or stratum containing oil, the attrition of the working or accumulating surface 24 on the wall formation 25 causes the oil film to be rubbed from the ends of the conducting elements, therebv reestablishing the low resistance circuit to ground. Thus, successive instantaneous readings on the indicating instrument 36 provide a record at the surface of the earth from which deductions can be made as to the oil content of the successive strata traversed by the well 26. If desired, these readings may be automatically recorded and related to the depth at which they are taken by means well known in the art.

Tests have shown that the thickness of the oil film collected on the Working surface of the accumulating member 20 must be increasedas the diameter of the terminal ends of the conducting elements is increased if the bridging effect described above is to take place. It will be understood, therefore, that the diameter of the ends of the conducting elements'may be selected in accordance with the degree of sensitivity required of the apparatus. Thus, an apparatus carrying conducting elements having extremely fine tips will be able to detect the presence of oil in muds or other earth formations in relatively small quantities. On the other hand, where the ends of the conducting elements are of larger diameter, the sensitivity of the unit will be relatively less acute, and the readings obtained thereby will indicate the presence of larger quantities of oil.

According to the invention, therefore, a well may be surveyed by a sensing device having two sets of conducting elements having tips of different diameters, each set being connected in a separate indicating circuit, thereby to provide readings indicating the approximate quantities of oil contained in each part of the well traversed.

It will be understood that the operation of the device as described above, is dependent upon the resistance value of the electrical circuit and accordingly it is within the scope of the invention to provide various types of resistance or impedance measuring devices in lieu of the ammeter indicated generally at 36. Thus, for example, a Wheatstone bridge or similar bridge circuit may be connected with one of the branches of the bridge comprising the circuit including the detecting apparatus.

In the embodiment shown in Figs. 5 to 7, inclusive, an accumulating member is used which is adapted for rolling, rather than sliding engagement with the wall of the bore hole. In these figures, apparatusas indicated generally at 39 is provided, which includes an elongated and weighted carrier 40 suspended by a cable 41 in the manner described above. Pivotally secured to the upper end of the carrier at the point 42a is a first arm 42 and a second arm 43 is pivotally received in a slot 44 formed in the lower end of the carrier. The two arms 42 and 43 are formed with bifurcated ends which are joined in a pivotal connection at 45, which pivot forms an axle for a wheel orroller detecting member 46 described below.

A tension spring 47 is connected between the upper and lower ends, respectively, of the arms 42 and 43 which urges the roller outwardly into peripheral engagement with the wall of the well. Thus, as the assembly 39 is lowered into the well, the roller 46 will roll along the walls thereof.

As shown in enlarged scale in Figs. 6 and 7, the roller 46 is formed of a pair of opposed metallic side wall members 48 and 49, formed with hub portions 50 and 51, respectively, by means of which the roller is rotatably mounted in the bifurcated ends of the articulated arms 42 and 43. Embraced by the wall members 48 and 49 is a central body member 52 formed of material having a particular affinity for oil in an aqueous medium, as described above.

Within the body member 52 is embedded a disc of electrically conducting foil 53 having a multiplicity of radial fingers or conducting elements 53 extending to the periphery of the body 52. Thus, it will be apparent that the periphery of the roller 46 is essentially similar to the working surface 24 of the rubbing member described above with reference to Figs. 1-4. The assembly of the roller 46 may be secured by means of three transverse screws 54 suitably insulated from the foil 53, for example.

The hub portion 51 of the roller 46 is preferably formed with an axial bore 55 which receives an insulating extension 56 formed on the body member 52. The extension 56 is also provided with an axial bore which receives an insulated electrical conductor 57, the inner end of which engages the foil 53 in an electrical contact at 57. The conductor 57 extends ultimately to the surface of the earth to'a source of voltage and-a current measuring device all as describedabove in connection with- Figs. 1-4, inclusive.

The operation of this apparatus is essentially the same as that of the apparatus described above with the exception that the sensing member rolls over instead of rubs against the wall of the well. I This mechanism affords certain advantages in that the rate of wear is decreased. Moreover, the roller is entirely exposed to the drilling mud which is usually quite homogeneous and of relatively low resistivityas compared with the earth formations. Since 'the detecting surface is in contact with either the drilling mud, or on. occasion,- WithOil contained therein, the indications obtained are generally more distinct and less influenced by variables such as the resistivities of the adjacent earth formations.

A further embodiment of the invention is shown. in Figs. 8 and 9. In this embodiment, a roller 58 is provided which comprises a central, electrically conducting center portion 59 having a plurality of relatively large radial tips or points 60 extending to the periphery of the wheel, the central portion being embraced by a pair of insulating side walls 61 and 62. Between the points 60 is disposed a material having an afiinity for oil, as indicated above. The roller 58 is rotatably supported on an axle 63 between a pair of spaced apart arms 64 and 65 formed on one of the carrier legs for the roller, the other having been omitted from the drawing for purposes of simplification. The general assembly for supporting the roller may be similar to that described above with reference to Figs. 57.

Received between the arms 64 and 65 above the axle of the roller is an insulating block 66 having a channel 67 formed therein for receiving the periphery of the roller with close lateral clearance. Pivotally supported by the insulating block 66 and partially recessed therein are a pair of insulating members 68 and 69, the free ends of which are urged downwardly against the periphery of the roller by means of springs 70 and 71, respectively. The width of the pivoted insulating members 68 and 69 may be substantially equal to the width of the channel 67 so that a closed area or cage is formed by the inner surface of the channel 67, the periphery of the wheel 58 and the pivoted insulating members 68 and 69.

Embedded in the insulating block 66 and extending for a short distance into the closed cage area as defined above, are a pair of spaced-apart electrical conducting elements 72 and 73. The lower ends of the conducting elements are disposed closely adjacent the periphery of the roller. The conducting elements 72 and 73 are connected by suitable conductors 74 and 75, respectively, to the surface of the earth. A source of voltage 74' is connected in series with conductor 74 and a suitable voltage measuring device 75 is connected in series with conductor 75. The voltage source 74' and measuring device 75' are connected to ground at 76.

In operation, the roller 58 will roll along the wall of the well and will carry small samples of the material comprising the wall into the closed cage. When no oil is present in the cage, a relatively good electrically conducting circuit to ground obtains through the conducting center portion 59, so that the voltage drop between the conducting element 73 and ground is low. When a film of oil is present on the roller, the resistance to ground will increase as will correspondingly the potential between the conducting element 73 and ground. The voltage drop sensed by the conducting element 73 is recorded by the meter 75', and thus affording an indication of the presence or absence of oil.

In this embodiment of the invention, the conducting points 60 of the conducting center portion 59 should be comparatively large in area so that their exposed surfaces will afford a comparatively low resistance path to ground when they are not wetted with oil.

A further modification of the invention is shown in Figs. 10 and 11, which embodiment comprises a weighted carrier element 77 suspended by a cable and insulated conductor indicated generally at 78. The carrier 77 supports an upper arm 79 by means of a fixed pivot 80. It also supports a lower arm 81, the lower end of which carries a pivot 82 received in a vertical slot 83 formed in the lower end of the carrier. The outer ends of the arms 79 and 81 are joined together in a pivotal connection at 84, which forms the axis of rotation of a roller 85. The roller is urged outwardly against the wall of the well by means of a tension spring 86 connected between the arms 79 and 81 as shown. Journalled in each of the arms 79 and 81- are rollers 87 and 88, respectively, which rollers are similar in construction to the roller 46 as shown in Figs. 6 and 7 and described in detail above.

As shown in Fig. ll, the roller comprises a pair of abutted, disc-shaped metal side sections 89 and 90 formed with an annular or peripheral channel 91 which receives an annular insert 92 formed. of material as described above having an affinity for oil in aqueousmedia. The sensing rollers 87 and 88, respectively, engage the peripheral insert of the roller 85 at circumferential spaced points and pick off the accumulated oil film therefrom.

The rollers 87 and 88 are identical with the one exception, namely, that one carries conducting elements 53 (Fig. 7) of smaller cross-sectional area at thetips than 7 does the other. It will be understood, therefore, that one of the wheel surfaces will be considerably more sensitive to the presence of oil than the other, this for the reason that the probes of one roller will become insulated from ground by the oil film before the other. Each of the rollers 87 and 88 is connected electrically to indicating or recording apparatus at the surface of the earth by independent conductors (not shown) in a manner similar to that described with reference to Figs. -7.

When the apparatus is in action and the roller 85 is in engagement with the well wall, it carries material picked up from the wall of the well into engagement with each of the rollers 87 and 88. As oil is encountered, an oil film builds up on each, first bridging the probe tips on the periphery of the wheel having the smaller conducting tips or points. The corresponding measuring or recording apparatus will indicate a variation in the resistance value of its circuit and it will be apparent to the operator at the surface of the earth that oil is present in a pre-established amount which is less than is required to actuate one system but sufficient to actuate the other. Of course, the number of sensing rollers may be increased according to the requirements of the system, and the diameters of the probe tips may be widely varied.

The particular forms of the invention described above and illustrated in the drawings are presented merely as examples of how the invention may be applied, and should not be construed as limiting in any way the breadth of the invention embodied therein. It will be appreciated, for example, that the electrical or measuring circuits used in obtaining readings as well as the design of the sensing members may be widely varied to suit the needs of each particular installation. Also, instead of grounding the energizing or measuring circuit at the surface of the earth, a ground might be provided by an electrode disposed in the well in the neighborhood of the apparatus.

Moreover, it is to be understood that the phraseology and terminology employed therein is used for purposes of description of the invention and not limitation. Other forms, embodiments and applications of the invention coming within the proper scope of the appended claims will readily suggest themselves to those skilled in the well surveying and analogous arts.

I claim:

1. Apparatus for detecting the presence of oil in a conducting medium including, in combination, accumulating means including a member having portions having an affinity for oil in the conducting medium for separating oil therefrom, said member having other portions which are electrically conducting and which are positioned with respect to the portions having an afiinity for oil as to be covered by accumulated oil, electrical circuit means including the electrically conducting portions of said accumulating means, and, in series therewith, the oil film which might be accumulated by the said portions having an afiinity for oil, and means responsive as a function of the electrical resistance of said electrical circuit means for indicating the presence or absence of oil on said member.

2. Apparatus for detecting the presence of oil in an electrically conducting medium comprising, in combination, accumulating means including a member having an affinity for oil in the conducting medium for separating oil therefrom, electrical conducting means associated with said member and adapted to be brought into electrical connection with said conducting medium, said electrical conducting means and said member being constructed and arranged relatively to one another to cause the oil as separated from the medium by said member to be interposed between the medium and the electrical conducting means, and means instantaneously responsive to changes in the electrical resistance of the circuit including the medium and the conducting means for indicating the presence or absence of oil on said member.

3. Apparatus for detecting the presence of oil in an aqueous medium including, in combination, a member having a surface formed of material having an afiinity for oil in an aqueous medium and adapted to be exposed to the medium, electrical conducting means embedded in said member and adapted to be brou ht into electrical contact with the aqueous medium, said electrical conducting means being disposed relatively to the member to be electrically insulated from the medium when oil is accumulated by the member, means for impressing a -8 voltage across said electrical conducting means and said aqueous medium, and means responsive as a function of the current flow between said electrically conducting means and said medium as indicative of the possible presence of oil on said member, the oil as accumulated on said member acting to insulate said electrical conducting means from said medium.

4. Apparatus for detecting oil as set forth in claim 3, said electrically conducting means embedded in said member comprising one or more electrical conducting elements, 2. terminus of each 'of which is disposed substantially flush with the working surface of said member and is adapted to be bridged by the film of oil which may be accumulated on said Working surface.

5. Apparatus for detecting oil as set forth in claim 3, said electrical conducting means comprising a dispersion of electrically conducting particles embedded in said member to render it at least a partial electrical conductor, the material of which the member is formed having an afiinity for oil in an aqueous medium, said memberbeing constructed and arranged to collect in the presence of oil in an aqueous medium a continuous film covering said member and affording an insulator in the electrical circuit including the electrical conducting means and the medium.

6. A method for detecting the presence of oil in an aqueous medium contained in a well comprising moving through the aqueous medium a member having portions having afiinity for oil in an aqueous medium and portions which are electrically conducting, impressing a voltage across said member and the aqueous medium, and measuring the current flow between the member and the aqueous medium to obtain values indicative of the presence or absence of oil on said member.

7. A method for detecting the presence of oil in earth formations traversed by a well containing an aqueous medium, comprising rubbing along the Wall of the Well a member having portions having an affinity for oil in aqueous media and portions which are electrically conducting, impressing a voltage across said member and the aqueous medium and measuring the current flow between the member and medium as indicative of the possible presence of an insulating layer of oil on the surface of said member.

8. A method for detecting the presence of oil in earth formations traversed by a well containing an aqueous medium, comprising picking off successive samples of the medium along the wall of the well, conveying the samples into an insulated cage to which said medium has access, impressing a voltage between a point in the ca e and a point outside the cage, and measuring the potential difference between a point in the cage and a point at a reference potential.

9. A method for detecting the presence of oil in a given electrically conducting medium, comprising exposing a member having portions which are electrically conducting and portions having an affinity for oil in the given medium to the medium to be analyzed, and obtaining indications of the electrical resistance of a path including in series said member, possibly accumulated oil, and the medium.

10. Apparatus for detecting oil in earth formations traversed by a well containing an aqueous medium including, in combination, an accumulating member adapted to be lowered into a Well and being formed with a working surface, said working surface including non-electrically conducting portions having an affinitv for oil in the medium, means for urging said working surface into engagement with the wall of the bore hole, electrical conducting means embedded in said member and having ends disposed closely adjacent said working surface, means providing electrical connections for impressing an electrical potential across said conducting means and the medium, and means responsive as a function of the resistance of the circuit including said conducting means and the medium for indicating the presence of oil in the medium, the oil accumulated on said working surface being interposed in said circuit to change the resistance value thereof.

11. Oil detecting apparatus as set forth in claim 10, said accumulating member comprising a roller, the peri heral p rtions of which comprise the workin surface havin an afiinitv for oil in the medium. and said electrical conduc ing means including a plurality of radially disposed fingers embedded in said material and having their terminal portions flush with the peripheral working surface or" said member.

12. Apparatus for detecting oil in earth formations traversed by a well containing an aqueous medium, comprising, a support adapted to be lowered into a Well, an arm member, means securing one end of said arm memher to said carrier member in a pivotal connection, means including a pin and slot connection joining the other end of said arm member to said carrier member to afford lateral displacement of said arm member, an accumulating member including a body portion of non-electrically conducting material carried by said arm member and being formed with a working surface for engagement with the wall of the bore hole, said working surface having a greater affinity for oil than for said medium, electrical conductor means embedded in said accumulating member and having ends disposed closely adjacent said working surface, spring means for biasing said arm member to urge said accumulating member against the Wall of the bore hole and electrical means for providing indications of the electrical resistance in a path including said conducting means and the medium.

13. Apparatus for detecting the presence of oil in an aqueous medium, comprising, a roller member including a circular portion formed of a non-electrically conducting material having an afiinity for oil in aqueous media and having a peripheral working surface, electrical conducting means embedded in said circular portion including a plurality of spaced apart conductors at the periphery thereof disposed substantially flush therewith, means for bringing a said roller into peripheral engagement with a medium to be analyzed, means for impressing an electrical potential across the embedded electrical conductive means and the medium, and means responsive to current fiow between said conducting means and the medium as indicative of the presence or absence of a film of oil on the periphery of the wheel, said circular portion being adapted to accumulate an oil film for bridging the electrical conductors at the periphery thereof to insulate them electrically from the medium.

14. Apparatus for detecting the presence of oil in an aqueous medium as set forth in claim 13, including a carrier member adapted to be suspended in a well, means for rotatably mounting said roller member on said carrier, and resilient means reacting between said roller member and said carrier for urging the roller member into peripheral engagement with the Wall of the well.

15. Apparatus for detecting the presence or" oil in an electrically conducting fluid medium, comprising, a first accumulating member having a working surface formed of a non-electrically conducting material having an aifinity for oil in the conducting medium and also having a plurality of electrical conductor means associated therewith and partially exposed on said working surface, a second accumulating member having a working surface formed of material having an afifinity for oil in the conducting medium and having a plurality of electrical conductor means associated therewith and partially exposed on said last-named working surface, the exposed electrical conductor means of each of the electrical conducting means in the first accumulating member having a larger exposed area than the electrical conductor means in the second accumulating member, the conductor means of one of said accumulating members thereby being adapted to be insulated from the conducting medium by a film of oil prior to insulation of the other from the conducting medium, and means individually responsive as a function of the resistance values of the respective circuits including the first accumulating member and the medium and the second accumulating member and the medium, thereby to afford a quantitative indication of the quantity of oil dispersed in the medium.

16. Apparatus as set forth in claim 15, said first accumulating member comprising a first roller member, said second accumulating member comprising a second roller, and a third roller member in engagement with the first and second rollers and adapted to engage the wall of an oil well to carry the media adjacent the wall of the well to each of said first and second rollers, said third roller member having a peripheral portion formed of a material having an affinity for oil in an aqueous medium.

17. Apparatus for detecting oil in an aqueous medium in an oil well comprising, a carrier adapted to be lowered into a well, a first roller member on the carrier and adapted to roll along the wall of the well to pick up matter disposed thereon, a first accumulating member comprising a second roller adapted to engage the first roller at a point spaced from the wall of the well, a second accumulating member comprising a third roller adapted to engage said first roller at a point spaced from the Wall of the well and spaced from the point of engagement of said first and second rollers, said first, second and third rollers having peripheral surfaces formed of a non-electrically conducting material having an affinity for oil in an aqueous medium, a plurality of electrode means embedded in each of said second and third rollers having termini flush with the peripheral surfaces thereof, the terminus of each electrode means in one roller exceeding in area the terminus of each electrode means in the other roller, and means responsive as a function of the electrical resistance between each of said rollers and the medium, respectively, the termini of the electrode means in one roller being adapted to be bridged by an insulating barrier of oil when a first given quantity of oil is present in the aqueous medium under analysis and the termini of the electrode means in the other roller being adapted to be bridged by an insulating barrier of oil when a second given quantity of oil is present in the aqueous medium under analysis.

18. Apparatus for detecting oil in a given medium comprising, a roller member carried by a support and adapted to be rolled along the wall of the well, insulating means cooperating with said roller member to form an enclosure, a pair of spaced apart electrode means disposed in said enclosure closely adjacent said roller member and in fixed relation thereto at a point spaced from the wall of the Well, means for impressing a voltage between one of said electrode means and a reference point and means connected to the other electrode means for measuring the voltage drop between said first electrode means and a point at a reference potential.

19. Apparatus for detecting oil as set forth in claim 18 in which said insulating means includes an insulating block carrying said electrode means, and formed with a channel to receive a portion of the periphery of said roller, a pair of insulating arm members disposed on opposite sides of said electrode means and supported by said insulating block, said arm members being adapted to bear against the periphery of said roller to provide a cage for said probes and into which the medium to be analyzed can pass.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 380,842 Williamson et al. Apr. 10, 1888 412,924 Kester Oct. 15, 1889 2,087,714 Wiles July 20, 1937 2,192,404 Jakosky Mar. 5, 1940 2,307,887 Haynes Jan. 12, 1943 2,422,852 Ratcliffe June 24, 1947 2,459,196 Stewart Jan. 18, 1949 2,604,785 Woestmeyer July 29, 1952 2,613,302 Gurewitsch Oct. 7, 1952 2,63 6,962 Bouyoucos Apr. 28, 1953 

